1. Technical Field
The present invention relates to a capacitive load driving circuit and driving method and a liquid drop ejecting device, and in particular, to a capacitive load driving circuit and driving method and a liquid drop ejecting device in which the amount of generated heat can be suppressed.
2. Related Art
There has been proposed a liquid drop ejecting device which applies an electric signal to a recording head having a piezoelectric element, converts the electric signal into a pressure wave, and ejects a liquid drop due to the pressure wave. The piezoelectric element provided at the recording head of the liquid drop ejecting device has electrostatic capacity in the same way as a capacitor. Therefore, when a large number of piezoelectric elements are driven simultaneously, Joule heat is generated from the resistance, and heat energy is lost.
Thus, a method of driving a liquid jetting recording head has been known, in which the voltage pulse which is applied to a piezoelectric element is plural, continuous, rectangular pulses P1, P2, . . . Pn−1, Pn of a given peak value V1 in a predetermined time period T1, and at least some of the intervals of applying the pulses P1, P2, . . . Pn−1, Pn and/or the pulse widths are made to be different.
However, when the interval or the pulse width at which the voltage pulses are applied is changed, there is the concern that it may be difficult to form a highly-detailed image. Thus, the amount of generated heat must be suppressed without changing the interval or the pulse width at which the voltage pulses are applied.
FIG. 10 is a circuit diagram showing the structure of a conventional piezoelectric element driver circuit. FIG. 11 is a timing chart showing the on signal inputted to the conventional piezoelectric element driver circuit, and the output waveform. When the on signal is low level, a PMOS is on, and 20 (=HV1) V is applied to a piezoelectric element 40. On the other hand, when the on signal is high level, an NMOS is on and the piezoelectric element 40 is 0 V.
FIG. 12 is a diagram showing the amount of heat generated at each point in shown in FIG. 11. Note that the electrostatic capacity of the piezoelectric element 40 is C, and the time at each point, i.e., the time constant, is 2 μs. In this way, heat of (½)C(HV1)2 [J] is generated in charging or discharging of one time. Accordingly, if an attempt is made to drive a large number of the piezoelectric elements 40 simultaneously, there is the problem that the amount of generated heat also increases in accordance therewith.